Blazor vs. React: Choosing a frontend framework

The introduction of WebAssembly (Wasm) has allowed developers to build web front ends in languages such as C#, C++, Rust, and Go. You can now compile your code from these languages into Wasm code that then gets compiled by the user’s browser into platform-agnostic machine code, meaning you no longer have to do all your frontend development in JavaScript. 

Blazor is a frontend framework that makes use of this to develop single-page applications (SPAs) in C# and run them using Wasm. This makes it an interesting fit for full-stack .NET developers who want to write front ends in their language of choice, and a strategic fit for companies heavily invested in the Microsoft ecosystem that want developer consistency across the stack. 

But how does WebAssembly compare to React, a JavaScript-based frontend library that’s currently the most popular library for building SPAs? This article compares Blazor vs. React, exploring their strengths, use cases, and differences. 

Overview of Blazor and React

Both Blazor and React are used to build SPAs but they come from different ecosystems. 

React is a popular JavaScript UI library currently dominating modern frontend development. It's interesting to note that React can (and arguably should) be used with TypeScript, a statically typed superset of JavaScript developed by Microsoft (allowing type safety). 

Blazor can be seen as a natural progression from this, as it was developed by Microsoft to allow developers to build frontend applications in C# and .NET using WebAssembly, allowing C# developers to write both frontend and backend code in a single, statically typed language.

What is Blazor?

Blazor is a frontend framework, maintained by Microsoft, that allows you to build SPAs with C# and Razor syntax. It integrates into ASP.NET Core and offers two different ways to run your app:

• Blazor WebAssembly: The app runs entirely in the browser via WebAssembly.

• Blazor Server: Most of the logic is run on the server. The browser renders the UI and communicates user interactions back to the server in real time using SignalR (a .NET communication library).

Blazor offers many modern frontend features out of the box, and it uses an optimized render tree to efficiently update the DOM, improving performance by avoiding unnecessary re-renders. Components support local state, allowing interactivity without having to rely on external libraries.

Blazor provides hot reload for developer productivity, allowing fast iteration. It also offers lazy loading, which can reduce initial load time, and built-in virtualization for rendering long lists. Blazor has gRPC-Web support, which can offer faster, more efficient communication than REST APIs for some scenarios. It uses Razor syntax instead of JSX/TSX, and avoids the need for JavaScript entirely.

One of the main pros is that developers can use existing .NET libraries and tools that they are familiar with. Blazor also has support for dependency injection: Web developers can inject services (like data access, state management, or logging) directly into components, promoting a modular and extensible application structure. In contrast to how React uses props and hooks for component communication or state management, .NET developers used to enterprise-style development will likely find Blazor with dependency injection a more natural way of doing things.

Blazor is a good choice for development if your team is already experienced in C# and the .NET framework, as it will allow your team to go full stack and use C# for both backend and frontend development.

What is React?

React is a frontend JavaScript library, maintained by Meta, and it can be used as a framework by adding extra packages and functionality or by adding a React framework like Next.js or Remix. It's the most popular UI library out there and has a thriving ecosystem and community.

React uses a virtual DOM, which only updates the parts of the UI that have changed, making it fast and efficient. React popularized component-based web development, which allows for modularity, and is very flexible with how you structure your projects, making it attractive to beginners and experts alike.

It has built-in hooks (```useState```, ```useReducer```, ```useContext```) for state management to allow interactivity. Later iterations have introduced React Server Components, currently available via the Next.js framework, that allow you to offload some UI logic to the server for performance gains.

Performance and rendering

Blazor WebAssembly can take a while to load on startup; you have to download the entire .NET runtime (especially slow for older devices or bad connections). It's important to note that this isn't the case for Blazor Server, which runs the app on the server and streams UI updates to the browser.

React apps often have a smaller client-side bundle size compared to Blazor WebAssembly, and developers can make a choice between different rendering strategies:

• Client-side rendering: This will load minimal HTML upfront and then hydrate the UI in the browser, which makes it faster than Blazor WebAssembly but can be slower if poorly optimized.

• Server-side rendering: This renders the initial HTML on the server, making the first UI paint faster, and then hydrates on the client (often used with frameworks like Next.js or Remix).

• React Server Components: This is a newer concept (currently closely tied to Next.js) where parts of the component run only on the server; this reduces client bundle size and allows developers to keep data-heavy components server side to reduce load times.

Where React allows for hybrid rendering models (CSR with SSR), Blazor requires you to pick one hosting model and stick with it.

React SSR and Blazor Server might seem similar, but there is a key difference: React SSR sends pre-rendered static HTML, and then hydrates it. Blazor Server, on the other hand, runs the component logic on the server and then pushes UI updates to the browser. It's a live connection model, rather than a static render and hydrate cycle.

The bottom line: React is generally faster for frequent DOM manipulations due to its Virtual DOM and the fact that it's JavaScript. Blazor can be slower for UI updates: Browsers run in JavaScript, and WebAssembly just adds another layer in between, which is going to cause latency.

However, although Blazor is slower for UI updates, WebAssembly makes it faster for heavy computation that doesn’t use the UI, because it can perform the calculations in native machine code. So, Blazor can be faster if your use case involves a lot of background computation and only occasional changes to the UI.

Blazor WebAssembly also offers an optional feature called AOT (ahead-of-time) compilation, which can improve performance by compiling languages like C# to a format that can be run by WebAssembly ahead of time. This can speed up execution for some things (compute-heavy workloads), but can increase download size and startup time. It's left up to you to decide whether it's worth enabling this from project to project.

Interoperability and ecosystem

React has a thriving ecosystem with thousands of npm packages and tools that you can use to extend its capabilities. It's intentionally minimal at its core, but, among many other choices, you can integrate with tools like Redux for global state management, Next.js for server-side rendering and routing, or Vite for fast bundling and prototyping. The stripped-back nature and modularity of React allows you to make custom choices about your tech stack and how to scale your application.

Blazor, designed to be more of an all-in-one framework, has more features out of the box, such as routing, form handling, and preconfigured HttpClient for API calls, among many other features. Blazor also integrates well with server-side .NET ecosystem libraries like Entity Framework or SignalR.

On top of this, Blazor has interoperability with JavaScript: You can call JS functions from C# via IJSRuntime. This interoperability is good for using browser APIs or libraries not yet available in Blazor and integrating with third-party JavaScript libraries (such as for charts or maps).

Developer experience and tooling

Both Blazor and React offer strong developer tooling. Their experiences, on the other hand, are different, based on the fact that they are from two different ecosystems and languages.

React is flexible and unopinionated. It integrates well with modern tooling like VS Code, Visual Studio, Vite, and TypeScript. It has access to extensive npm libraries, features such as fast refresh and React Developer Tools (for help with debugging), making it easy to work with and popular among frontend developers.

Blazor also works well with VS Code and Visual Studio. It offers dev features like hot reload for Razor components and code sharing between the back end and front end (e.g., sharing data models or DTOs), which is a major productivity boost for .NET developers. With React, you need to integrate TypeScript for type safety, whereas Blazor supports type-safe development out of the box with C#'s mature type system.

SEO: Blazor vs. React

Some teams hesitate to build single-page applications because, although there is a jump in performance and user experience, pages can suffer from poor SEO when built using traditional methods like client-side rendering (CSR), as web crawlers may struggle when attempting to index content rendered in JavaScript, or experience delays in doing so. Rendering strategies such as server-side rendering (SSR) and static site generation (SSG) can fix this problem, as the server sends fully rendered HTML to the browser, allowing search engine crawlers to immediately see the content (no need to run JavaScript first).

With React, you can easily use SSR and SSG, among other SEO-friendly rendering strategies (like ISR) by using Next.js (a React framework), which offers these rendering methods out of the box. You can even apply these strategies on a per-page or per-component basis, meaning you might decide to use SSR for your marketing or blog pages (when SEO and performance are important) but use CSR for your more interactive components that rely on client-side state, such as admin dashboards or in-browser editors.

Blazor WebAssembly apps are entirely client side, which makes SEO much harder. If SEO is a priority, then you can use Blazor Server, which uses a live SignalR connection to interactively update the DOM rather than sending a complete HTML snapshot at request time. However, this model still doesn’t offer the full SEO benefits of frameworks like Next.js. While Blazor Server is better than Blazor WebAssembly for SEO, it's not ideal for marketing pages, where you would benefit from per-page static generation.

Testing and debugging: Blazor vs. React

React has a whole host of testing frameworks, such as Jest and React Testing Library, and Cypress for end-to-end testing. You can also integrate React dev tools into the browser to catch bugs and view application state as you code.

Blazor has tools for testing with frameworks like xUnit and bUnit for component testing. You can also cover end-to-end tests with frameworks like Playwright or Selenium (also compatible with React). Blazor has limited debugging tools, especially Blazor WebAssembly. Browser debugging is possible via Chrome dev tools or Visual Studio, but the experience isn't as smooth as JavaScript's native integration with browser consoles.

Use cases, community, and popularity

React is the most popular and widely used frontend library in the world. You can use it to build interactive web apps, content-heavy dashboards, static marketing pages, and even mobile applications with React Native. Companies like Meta, Airbnb, and Netflix use React in production. Its vibrant community ensures a steady flow of libraries, tutorials, and support.

Blazor is a newer framework, but is starting to gain traction, especially in teams that already use .NET. Use cases include internal tools and line-of-business apps. Companies like Dell, Stack Overflow, and Raygun have adopted Blazor for various projects. Its main appeal is for organizations that want full-stack C# development and integration with ASP.NET infrastructure.

In the latest Stack Overflow survey, in the section on most popular frameworks, React tops the chart for frontend frameworks with 39.5% of respondents having used it, whereas Blazor is further down the chart with 4.9%.

Choosing between Blazor and React

As with choosing between any language or framework, you need to understand what kind of application you're building. Is it an internal tool? Or is it a customer-facing app? Is SEO important, or does performance matter more? More specifically, when choosing between Blazor and React, it makes more sense to choose Blazor if you need to integrate with existing .NET systems, or your team is already working with C# and doesn't have a lot of experience with JavaScript or TypeScript.

Below is a table to help you visualize how Blazor and React compare on a few important metrics:

Whether Blazor or React — Contentful delivers your content

React is more integrated with Contentful tooling. Contentful provides a number of React SDKs to help you build content-focused apps. The documentation and ecosystem also offer starter templates to help you get your project up and running in no time. React is a great fit for building content-focused apps with its hybrid rendering model and compatibility with composable content platforms like Contentful.

Whether you choose to use Blazor or React, you can save time by using Contentful as a headless content management system. No need to code an admin dashboard from scratch, or set up a CMS with a database — Contentful can provide all of this and deliver your content via HTTP or GraphQL from its high-speed CDN.

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